The recording density of a magnetic hard disk is potentially superior to that of an optical disk. It is also easier to reduce the price of a magnetic head than of an optical head because of the simple structure of the former. In industry, however, it is no easy matter to decrease head flying height from the submicron to the sub-submicron level because of head/media wear durability. Tribologv is the most important factor in the future development of magnetic disk stroage devices.